1. Technical Field of the Invention
The present invention relates to an apparatus for stabilizing food products prior to freezing thereof.
2. Prior Art
Cold-air freezers using a relatively slow air flow are very cost-effective in that their energy consumption is relatively low. Freezers of this type are described in e.g. U.S. Pat. Nos. 4,603,776 and 4,953,365, the disclosures of which are incorporated herein by reference. The cooling rate in such freezers is moderate, but this is often no disadvantage because the internal heat conduction of the products to be frozen sets an upper limit to that rate. This is particularly true for thick products.
To some extent, the cooling rate can be increased by means of impingement freezing, i.e. high-speed cold-air jets that break through the air layer closest to the surface of the products to be frozen, thereby improving the heat transfer. Such an increased cooling rate may be highly beneficial for thin products, but requires a greater consumption of energy.
Increasing the heat transfer at the beginning of a freezing cycle results in a frozen crust forming quickly at the boundary of the product, which means less dehydration of the frozen products. Creating such a crust therefore increases the yield.
The use of impingement freezing in a cold-air freezer is described in U.S. Pat. No. 5,203,802. The disclosure of this patent is incorporated herein by reference. However, product quality for some products is still decreased as a consequence of product sticking to a conveyor belt, resulting in damage to the product at the outfeed end of the freezer when the product is lifted off the conveyor belt.
U.S. Pat. No. 5,156,008 describes a method of freezing a crust on food products by placing them on a firm support of such extremely low temperature that the products will not freeze on to the support. This method requires the use of cryogenic gases in order to give the support an adequately low temperature and, therefore, it is not very cost-effective.